Monday, February 25, 2013

The hemichordates (phylum hemichordata) are worm-like animals characterised by a three-part body - the front end (the prosome), followed by a collar (the mesome) and a posterior trunk (metasome). There is a flexible, hollow tube (the stomochord) in the collar region, somewhat resembling the notochord found in chordates (animals with a spinal cord at least in part of their life cycles). In fact, "hemi" means "half" in Greek, while "chorda" means "chord" in Latin.

Hemichordates share many similarities with the chordates. For example, they have a circulatory system with a heart, and also gill-like structures similar to the gills of primitive fish. Studies, however, suggest that hemichordates are most closely related to the echinoderms, and this is further supporter by the fact that the larvae of some hemichordates appear very similar to those of some echinoderms.

The only group of hemichordates recorded from Singapore so far is the acorn worms (class Enteropneusta). The other valid class of extant hemichordates, class Graptolithoidea, were colonial animals with tentacles for filter feeding, i.e. they filter plankton and other tiny organic particles in the water.

Acorn worms are solitary worm-like animals that live in U-shaped burrows. While some species are filter-feeders, most of them are deposit feeders - they swallow sand or mud and digest the tiny organic particles inside. During low tide, they will stick out their back end, and excrete the processed sediment in coils (called cast).

In fact, the acorn worms themselves are hardly seen, and most of the time, only the casts left behind during low tide are seen. The cast, however, is very similar to the casts deposited by lug worms. It is often difficult to tell them apart just by looking at the casts without digging out the animal, and hence, the photo above could be the cast of either one.

Acorn worms have separate sexes, though some species are also able to reproduce asexually. The females lay eggs embedded in mucus, and the males will release the sperm over them, fertilising them externally. Depending on the species, the eggs may hatch into planktonic larvae, miniature adults or an intermediate free-swimming form.

References

Cameron, C. B., J. R. Garey & B. J. Swalla. 2000. Evolution of the chordate body plan: new insights from phylogenetic analyses of deuterostome phyla. Proceedings of the National Academy of Sciences of the United States of America 97 (9): 4469–74.

Comb jellies (phylum Ctenophora) are mostly free-swimming organisms that appear like jellyfish, though some species may not swim but instead creep over the substrate.

The free-swimming species usually appear transparent and somewhat rounded. Many come with a pair of tentacles fringed with smaller tentacles (or tentilla), and most have eight strips (called comb rows) running down the length of their bodies. Each strip bears bands of hair-like projections (or cilia) which resemble a comb, and hence the name Ctenophora (which means "comb carrying" in Greek) and the common name comb jellies. These free-swimming comb jellies swim by beating their celia.

The species that do not swim usually appear flatten, much like flatworms. Most of them lack the comb-row, but they possess a pair of tentacles much like many of the free-swimming species. See this photo from Wikimedia which features numerous worm-like ctenophores extending their long tentacles on a sea star.

Ctenophores are carnivorous, and use their tentacles to capture their prey, which include copepods, jellyfish and other zooplankton. Most species have special cells called colloblasts that discharge adhesive substances to stick and capture their prey. Those that feed on jellyfish may incorporate the latter's sting cells into their tentacles to sting their prey.

Reptiles (phylum Chordata, subphylum Vertebrata, superclass Tetrapoda, class Reptilia) are vertebrates (animals with a backbone and a hollow tube of nervous tissue called a spinal cord) characterised by their limited physiological means to maintain the body temperature within a narrow range, and their ability to produce water-tight eggs.

Being unable to maintain the body temperature within a narrow range (or being ectothermic) means that they are more reliant on external heat sources. Meanwhile, the water-tight eggs are better protected from the external environment compared to the eggs produced by amphibians and fishes. Other vertebrates which produce water-tight eggs include the birds and the mammals (though only a few species of extant mammals still produce eggs), and they are usually referred to as "amniotes". They are descended from four-limbed ancestors (hence the superclass Tetrepoda which means "four legs"). The birds and mammals are endothermic though, being able to generate body heat and maintain the body temperature within a narrow range. Also, birds and mammals are covered in feathers and hair/fur respectively, while reptiles are mostly covered in scales.

Most reptiles lay eggs (oviparous), though some species may bear live young (viviparous), or bear live young from eggs brood within the body (ovoviviparous).

Here are some of the reptiles that I have seen in Singapore:

A) ORDER SQUAMATA

The order Squamata comprises the lizards and snakes. They can be distinguished from other reptiles by their relatively slender bodies that are covered by scales; extremely movable upper jaws which allows them to swallow relatively large prey; and the males possessing penises that that in pairs (each called a hemipenis).

Lizards (suborder Lacertilia) are reptiles with a slender body covered by scales, four limbs (hence the superclass Tetrepoda which means "four legs") and a tail. Some species, however, may have very reduced limbs or no limbs at all. The legless species may resemble snakes, but unlike the latter, most lizards have eyelids and external ears.

Crocodilians (order Crocodilia) are semi-aquatic reptiles with a long snout, short limbs with webbed feet, and a muscular, laterally compressed tail. They have large and powerful jaws with conical teeth, allowing them to effectively hunt for fish and other animals. Their body is covered in tough and leathery plate-like scales. They have a special eyelid-like membrane which covers the eye when they are underwater.

Turtles (order Testudines or Chelonii) are air-breathing reptiles with four limbs, a tail, and an external shell modified from their ribs. The shell comprises a shield-like carapace on their back and a flat bony plate (plastron) protecting their bellies. When disturbed, they can either completely or partially withdraw the head, limbs and tail into the shell for protection.

Friday, February 22, 2013

Crocodilians (phylum Chordata, subphylum Vertebrata, superclass Tetrapoda, class Reptilia, order Crocodilia) are semi-aquatic reptiles with a long snout, short limbs with webbed feet, and a muscular, laterally compressed tail. They have large and powerful jaws with conical teeth, allowing them to effectively hunt for fish and other animals. They are good swimmers, and have a special eyelid-like membrane which covers the eye when they are underwater. Their body is covered in tough and leathery plate-like scales. Crocodilians usually lay their eggs in nests constructed of vegetation on land, guarded by the female.

Like most other reptiles, they have limited physiological means to maintain the body temperature within a narrow range, and are more reliant on external heat sources. Like other vertebrates, they have a backbone with a spinal cord (a hollow tube of nervous tissue).

The Estuarine Crocodile (Crocodylus porosus)is the only crocodilian that has been confirmed to occur in Singapore. This is the largest living species of reptile in the world, with reports suggesting that it can grow up to 9m long. Most of the ones seen are much smaller though. In Singapore, they are occasionally seen in mangrove forests, estuaries and reservoirs, and the ones sighted are not more than 3m long. They mostly hunt for fish and other small animals at night. In the day, they can be seen basking in the sun at the water's edge, or hiding among vegetation.

Estuarine Crocodiles have a long and relatively broad snout. The body is usually yellow, olive or greyish above with black checker-spots, while the underside is white. They start breeding when they are about 3m long. Crocodile nests constructed of vegetation has been discovered in our mangrove forests before, and young crocodiles have also been sighted.

Thursday, February 21, 2013

Turtles (phylum Chordata, subphylum Vertebrata, superclass Tetrapoda, class Reptilia, order Testudines or Chelonii) are air-breathing reptiles with four limbs, a tail, and an external shell modified from their ribs. The shell comprises a shield-like carapace on their back and a flat bony plate (plastron) protecting their bellies. When disturbed, they can either completely or partially withdraw the head, limbs and tail into the shell for protection.

The terms used to describe the various types of turtles can be confusing, but generally, the term "terrapin" refers to a turtle that is semi-aquatic, the term "tortoise" is used for land-dwelling species, while a "soft-shelled turtle" has a shell covered with soft, leathery skin.

Like most other reptiles, turtles have limited physiological means to maintain the body temperature within a narrow range, and are more reliant on external heat sources. However, some of the larger turtles have high metabolic rates, and hence they tend to have higher body temperature than their surrounding environment. Like other vertebrates, they have a backbone with a spinal cord (a hollow tube of nervous tissue). This backbone is fused to part of the carapace.

Turtles have separate sexes. The males will mate with the females, after which the females will lay the eggs in holes they have dug into the ground. The eggs will then be buried and left to incubate.

Here are some of the turtles that can be found in Singapore:

Family Cheloniidae

Cheloniid turtles are sea turtles with a hard shell and paddle-like limbs. The shell is relatively flat, giving the animal a streamlined shape. The shell is covered with horny, scale-like plates called scutes, while the head and limbs are partially covered with thin scales. The neck can only retract partially into the shell. They usually have a beak. Sea turtles are very much threatened by fishing activities, as many get trapped underwater by fishing nets. Being air breathing, they can suffocate to death underwater. Both the turtles and their eggs are exploited for food by locals. Interestingly, sea turtles can migrate long distances (up to a few thousand kilometres) between their feeding grounds to the sandy beaches where they are hatched to lay eggs. The females will crawl onto the beach at night, dig a nest into the sand, lay the eggs, bury them with sand, and leave them for incubation. The hatchlings will emerge within a few months. Many of them are eaten by predators on the beach and in the shallow water, and few will survive to adulthood.

The Hawksbill Turtle (Eretmochelys imbricata) is an internationally critically endangered sea turtle which usually inhabits coral reefs, lagoons, bays and estuaries. It feeds on sponges, algae, corals and molluscs. The carapace, which can get to about 1m long, is olive-brown in colour.

The Hawksbill Turtle can be differentiated from other sea turtles by its pointed bird-like beak, and two pairs of scales on its forehead between the eyes behind the beak.

The Green Turtle (Chelonia mydas), on the other hand, only has a pair of longish scales on its forehead between the eyes behind the short and broad beak.

The carapace, which can get to about 1.4m long, is olive or brown with radiating dark patterns. Green turtles are internationally endangered, and are usually found in tropical areas around islands and along coast with sandy beaches. The juveniles are carnivorous, while the adults feed on seagrass and seaweeds.

Family Trionychidae

Trionychid turtles are usually called softshell turtles, due to the soft carapace which is covered with a layer of leathery skin. They have three claws on their fully webbed feet, a long neck, and a tube-like snout with the nostrils at the tip. Although they may leave the water sometimes to bask in the sun, they are usually hidden in soft substrates, with their heads partially exposed to snap at the small animals in the water. They breathe by extending their necks regular to put the nostrils above the water. They can give very nasty bites, and hence should not be handled.

The Malayan Forest Softshell Turtle (Dogania subplana) has a smooth, flat and leathery carapace which can grow to about 35cm long. It is roughly oval-shaped and yellowish-brown in colour. The above photo features a juvenile, which has several black, eye-like spots on its carapace. The adults lack the obvious spots, but has blurry darker patches instead. The carapaces of both juveniles and adults are marked with irregular darker streaks and a darker stripe in the middle. They are usually found in clear streams with sandy bottoms in mature forests.

The Chinese Softshell Turtle (Pelodiscus sinensis) is native to China and Japan, but has been introduced to ponds and reservoirs probably through religious merit-making offerings. The carapace is oval-shaped, smooth and leathery, either uniformly brown or with pale and dark spots. There is a ridge at the front edge of of the carapace. The head is marked with black streaks radiating from the eyes, and a pale stripe marks the sides of the neck. This species is commercially bred in the region for consumption, and can grow to about 35cm long.Family Emydidae

Emydid terrapins are not native to the region, but as several species are popular in the pet trade, they have been widely introduced to many countries out of their native range. They have an oval to oblong domed carapace with 11 pairs of peripheral scutes around the margin. These terrapins are usually found in freshwater environment, at least in some part of their lives. They are mostly omnivorous.

The Red-eared Slider (Trachemys scripta) is native to North America, and the ones found in local water bodies are either escaped or abandoned pets (by irresponsible pet owners), or those released as religious merit-making offerings. The domed carapace, which is olive brown with yellowish streaks, can get to about 28cm long. The head is green with many yellow stripes, and a reddish band is located behind the eye. This diurnal and omnivorous species is mostly aquatic, though they can be seen basking in the sun sometimes.

Family Geoemydidae

Geoemydid terrapins are rather similar to the previous group, with an oval to oblong carapace with 11 pairs of peripheral scutes around the margin. The carapace can be depressed or domed. These terrapins can withdraw their necks into the shell. Most species are omnivorous, though some may begin as carnivorous juveniles, but become herbivorous as they mature.

The Malayan Box Terrapin (Cuora amboinensis) has a highly domed black carapace which can get to about 25cm long. The carapace has a smooth margin, and in its middle are five vertebral scutes. The head is black above, with a bright yellowish stripe on both sides. This terrapin is semi-aquatic to terrestrial, and can be found in agricultural areas and the edge of forests. It can be active both in the day and at night. While the Malayan Box Terrapin is native to Singapore, most of the ones seen in our reservoirs and ponds in parks are probably released illegally for religious merit-making offerings.

The Giant Leaf Terrapin (Heosemys grandis), also known as the Giant Asian Pond Turtle, is native to continental Southeast Asia, but is probably introduced to the ponds and reservoirs in Singapore through religious merit-making offerings. This big terrapin can grow to about 50cm long. It can be recognised by the blunt snout and greyish carapace.

The Chinese Stripe-necked Turtle (Mauremys sinensis) is native to China, Taiwan and Vietnam. This species can sometimes be seen in ponds, probably released illegally for religious merit-making offerings. It can be recognised by the yellow stripes on its neck.

Sunday, February 17, 2013

Lizards (phylum Chordata, subphylum Vertebrata, superclass Tetrapoda, class Reptilia, order Squamata, suborder Lacertilia) are reptiles with a slender body covered by scales, four limbs (hence the superclass Tetrepoda which means "four legs") and a tail. Some species, however, may have very reduced limbs or no limbs at all. The legless species may resemble snakes, but unlike the latter, most lizards have eyelids and external ears.

Lizards and snakes are of the same order, Squamata. They can be distinguished from other reptiles by their relatively slender bodies that are covered by scales; extremely movable upper jaws which allows them to swallow relatively large prey; and the males possessing penises that that in pairs (each called a hemipenis).

Like most other reptiles, they have limited physiological means to maintain the body temperature within a narrow range, and are more reliant on external heat sources. Like other vertebrates, they have a backbone with a spinal cord (a hollow tube of nervous tissue).

Depending on the species, lizards may lay eggs (oviparous), bear live young (viviparous), or bear live young from eggs brood within the body (ovoviviparous).

Many people dislike or even fear lizards, but most lizards are quite harmless and even help to control the population of insect pests in homes and gardens. Most lizards are also not venomous.

I have only seen some of the lizards that can be found in Singapore, and have photographed even fewer of them. I certainly hope to eventually see more species during my future trips so that I can update this blog post. Here are just some of those that I managed to photograph:

Family Varanidae

Varanid lizards, commonly called monitor lizards, are usually large lizards with sharp claws, a relatively long neck, a powerful tail, and a forked tongue, much like those of snakes. The tongue is extended every now and then to "taste" the air for the scent of food. Monitor lizards are mostly carnivorous, though a few species are known to be frugivorous (i.e. eat fruits). Studies have shown that some species of monitor lizards are venomous, and are closely related to snakes. They lay eggs with soft shells.

The Malayan Water Monitor (Varanus salvator) is one of the largest lizards in the world, being able to grow to about 3m long, though most are below 2m. It has thick and leathery skin with non-overlapping scales. Like other monitor lizards, it has a forked tongue.

The nostrils are positioned close to the tip of the snout. Young Malayan Water Monitors are black with yellow spots, while the adults are usually plain greyish brown. They can swim and climb very well, and are commonly seen in coastal areas such as mangroves, islands, and coral reefs. They are also often seen in agricultural areas, parks, canals, and reservoirs. During the breeding seasons, males can be seen fighting by standing on the hind legs and hugging each other, supported by the powerful tail, clawing at each other's back. Malayan Water Monitors feed on carrion or hunt for fishes and other small animals. They are often trapped by locals for their meat, which is consumed, and their hides, which can be made into leather products.

The Clouded Monitor (Varanus nebulosus) is smaller than the previous species, growing to about 1.7m long. Like other monitor lizards, it has and forked tongue, thick and leathery skin, and non-overlapping scales. Unlike the previous species, the snout is relatively short with the nostrils positioned midway between the eye and the tip of the snout. The skin is greyish brown in colour, densely marked with yellow spots. Clouded Monitors hunt for small animals by digging among the leaf litter with their sharp claws. They are usually found in the forests and scrubland.

Family Agamidae

Agamids generally have long legs and tails, but short heads. They have rough scales covering their bodies, and many species have a crest running down the head to the back of the body. They are usually diurnal and live in trees and bushes, descending to the ground only to move to another tree or to lay eggs. In many cases, the females bury their eggs in the soil. Most species feed on small animals, but some larger species feed on flowers, seeds and other plant parts as well.

The Changeable Lizard (Calotes versicolor) is an introduced species that is commonly seen in urban parks, scrubland and forest edges. It can change its colour, but not as dramatically or quickly as the chameleon. It is native to Peninsular Malaysia, Thailand and other parts of mainland Southeast Asia. Growing to about 38cm, this lizard has strongly keeled scales, a relatively large head, long slender limbs, a long tail and a spiny crest running down the back of its head to the back of the body.

This species is rather variable and changeable in colour, and can be yellow, green or brown (sometimes with darker patterns). Juveniles and females may have a pair of pale stripes along their backs.

It can be differentiated from similar species by the two spines above the ear opening. Male Changeable Lizards are bigger with swollen cheeks, and the heads turn orange during the breeding season. They can be seen nodding their heads and doing push-ups during this period to court the females and to deter rival males. Like other agamids, Changeable Lizards are oviparous.

The Green Crested Lizard (Bronchocela cristatella) is native to Singapore. While it is largely displaced by the previous species in urban areas and forest edges, it is still fairly common in parks that have many shrubs and trees, and in the forest. Growing to about 58cm long, it has a moderately slender body with small strongly keeled scales, long slender limbs, a very long tail, and a spiny crest at the back of its head.

Green Crested Lizards are usually bluish green in colour, but may change to dark brown, such as the male in the above picture, which changed from green to brown during courtship, but changed back to bright green after mating. They are diurnal, and are usually found on trees or bushes. The females bury their eggs in the soil.

The Common Flying Dragon (Draco sumatranus) is a gliding lizard which can glide from tree to tree. Growing to about 22cm long, it has a slender body with small scales, long slender limbs and a very long tail. The body is light brown, marked with darker and lighter blotches. There is a broad flap of skin (patagium) supported by ribs on both sides of its body which is black in colour with irregular brownish and greenish patterns. It glides by launching off into the air and extending its patagium, much like a gliding kite. The male has a bluish head and a large yellow throat flap, as featured in the picture above. The throat flap is usually extended for courtship purposes or to deter other males.

The female Common Flying Dragon lacks the bluish head, and has a much smaller throat flap. This oviparous species can be found in the forest, agricultural areas and parks.

The Black-bearded Flying Dragon (Draco melanopogon) grows to about 24cm long. Like the previous species, it has a slender body with small scales, long slender limbs and a very long tail. The back of the body is olive or green with greyish brown bars or blotches, while the patagium is black with many yellow spots. The throat flap of the males is black and orange, and hence the common name Black-bearded Flying Dragon. Like other gliding lizards, it can glide from tree to tree by extending the patagium at the sides of the body, and display the throat flap during territorial dispute or courtship. This oviparous species is usually found in mature forests.

The Five-banded Flying Dragon (Draco quinquefasciatus) grows to about 27cm, and is usually found in mature forests, often near water bodies. While it is also greenish in colour, it can be differentiated from the previous species by the five dark bands marked with numerous white spots across its back, and the pinkish-orange patagium. The throat flap of the male is yellow in colour, while those of the female is greenish with yellowish spots.

Family Gekkonidae

Gekkonid lizards, commonly called geckos, have thin and delicate skin with tiny scales and large eyes without movable eyelids. Most species are nocturnal, but some are diurnal or both. If they are caught by the tail, they are able to break it to escape while the broken tail continues to wriggle about to confuse the predator. A new tail will eventually grow to replace the lost one. Some geckos have expanded fingers and toes functioning like adhesive pads. The underside of these pads is lined a series of skin flaps with numerous microscopic hook-like hairs which allow the gecko to walk on vertical surfaces and even upside-down. Geckos are oviparous.

The Spiny-tailed House Gecko (Hemidactylus frenatus) is a very common gecko in human habitations, and sometimes in the forest. It can grow to about 13cm long, and like other geckos, has thin skin with tiny non-overlapping scales and large eyes without movable eyelids. The toes and fingers are expanded into adhesive pads. The colour of this lizard is rather variable, but is generally a pale greenish brown with irregular darker speckles. The tail has numerous spiky structures (tubercles). This oviparous gecko can be active both in the night and in the day, hunting for insects.

The Mourning Gecko (Lepidodactylus lugubris), also known as the Maritime Gecko, is quite widespread in Singapore though more commonly seen in coastal habitats. It can be seen in scrublands, coastal forests, mangrove forests, and sometimes in buildings. It can grow to about 10cm long, and like other geckos, has thin skin with tiny non-overlapping scales and large eyes without movable eyelids. The toes are expanded into adhesive pads. It has a pair of elongated black spots on the nape, and the top of the broad tail has a series of irregular black-edged yellowish bands. The colour of the body ranges from light to dark greyish brown with black flecks and whitish blotches. Interestingly, this is an all-female, oviparous species that reproduces by parthenogenesis, in which the embryos develop and grow without the need for fertilisation (hence it is a form of asexual reproduction). It is mostly nocturnal, and feeds on small arthropods as well as nectar and plant juice.

The Four-clawed Gecko (Gehyra mutilata) is commonly seen in human habitations and also wooded areas. It can grow to about 12cm long, and like other geckos, has thin skin with tiny non-overlapping scales and large eyes without movable eyelids. The toes are expanded into adhesive pads. The colour of the body is pinkish brown with gold and blackish flecks. The tail is smooth. This lizard is nocturnal and feeds on insects.

The Lowland Dwarf Gecko (Hemiphyllodactylus typus) is usually found in mangroves, scrublands and forests. It can grow to about 10cm long, and like other geckos, has thin skin with tiny non-overlapping scales and large eyes without movable eyelids. The toes are expanded into adhesive pads. The colour of the body is brown with dark markings. It has a prehensile tail (usually of a paler colour compared to the body) with a yellowish blotch at the base. It is nocturnal and feeds on insects.

The Kendall's Rock Gecko (Cnemaspis kendallii) is a forest species, and in Singapore is usually found in mature forests. It can grow to 14cm long, and like the previous geckos, has thin skin with tiny non-overlapping scales and large eyes without movable eyelids. The digits, however, are not expanded. It has a long snout that is slightly upturned. The pupils are distinctly rounded. The back of the body is yellowish with dark brown and white blotches. This oviparous gecko can be active both at night and in the day, feeding on insects on rock walls and trees.

The Peter's Bent-toed Gecko (Cyrtodactylus consobrinus) is usually found in mature forests. It is typically black or dark brown with whitish bands and net-like patterns. This rather large gecko can grow to about 28cm long. It is nocturnal, emerging to hunt small invertebrates at night.

Family Scincidae

Scincid lizards, commonly called skinks, generally have a smooth and slender body, short legs, and a long tail. They are usually covered in shiny scales, and the ones on the forehead are enlarged and usually symmetrically arranged. Some species live on the ground, while others may live on trees. Some ground species can also burrow, and these skinks tend to have short legs, or only two legs, or even no legs at all. A few species are semi-aquatic. Like the geckos, they can readily break off their tails to confuse predators, and grow new ones to replace the lost tails.

The Garden Supple Skink (Lygosoma bowringii) occurs in a variety of habitats, and can be seen in urban areas (in parks and among grasses), agricultural areas, and forests. It can grow to about 11cm long. The body is very slender and covered in shiny smooth or weakly keeled overlapping scales, bronze-brown in colour on the back and blackish with white spots on the sides. There is an orange patch behind each eye, and the large scales on the top of the head are symmetrically arranged. The limbs are orange in colour and are very small. This oviparous skink is a diurnal animal, and hunts for small invertebrates among the leaf litter and undergrowth, or in the soil.

The Many-lined Sun Skink (Eutropis multifasciata) has a robust body covered in shiny overlapping and strongly keeled scales. The large scales on the forehead are symmetrically arranged. The back is bronze-brown, and some may have a series of black lines. The sides of the body are either blackish or brown with white spots, or orange from the ear to the hind leg.

The above photo features one which has an orange band on each side of the body. Many-lined Sun Skinks can grow to about 35cm long. They are mostly terrestrial, and can be seen basking on the ground on sunny days. This ovoviviparous species can be found in a variety of habitats, such as inland forests, coastal forests, agricultural areas, parks and gardens. They feed on small invertebrates.

The Mangrove Skink (Emoia atrocostata) is rarely seen in Singapore. It occurs in mangrove forests and sometimes rocky shores. It can grow to about 26cm long, and is covered in smooth overlapping scales. The body is greyish brown with whitish spots above, and somewhat bluish with a blackish strip and whitish spots along the sides. The large scales on the forehead are symmetrically arranged. It is diurnal, and is usually found on the forest floor, on the roots or sometimes on tree trunks. This species is oviparous, and feeds on insects and small crustaceans.

Wednesday, February 13, 2013

Snakes (phylum Chordata, subphylum Vertebrata, superclass Tetrapoda, class Reptilia, order Squamata, suborder Serpentes) are legless reptiles with a long and somewhat cylindrical body. They resemble legless lizards, but lack the eyelids and external ears that most lizards possess.

Snakes and lizards are from the same order, Squamata, and they can be distinguished from other reptiles by their relatively slender bodies that are covered by scales; extremely movable upper jaws which allows them to swallow relatively large prey; and the males possessing penises that that in pairs (each called a hemipenis).

Like most other reptiles, they have limited physiological means to maintain the body temperature within a narrow range, and are more reliant on external heat sources. They are descended from four-limbed ancestors (hence the superclass Tetrepoda which means "four legs"), and have a backbone with a spinal cord (a hollow tube of nervous tissue).

Depending on the species, snakes may lay eggs (oviparous), bear live young (viviparous), or bear live young from eggs brood within the body (ovoviviparous).

Many people (including myself at one time) fear snakes, but most snakes are actually not aggressive unless provoked. If you keep a good distance and do not attempt to disturb them, they can be admired and observed. However, if the snake hisses or raises the front part of its body, it is probably disturbed and you should back off.

I still have not seen most of the snakes that are recorded from Singapore, and hope to eventually see more during my future trips so that I can update this blog post. Here are just some of those that I managed to photograph:

Family Typhlopidae

Typhlopids, also known as blind snakes, usually have very reduced eyes, a blunt and rounded snout, and a head that is indistinct from a cylindrical body. They also have a very short blunt tail, which ends in a spine for some species.

The Brahminy Blind Snake (Ramphotyphlops braminus) is a small blind snake (up to 18cm long) that has a black and smooth cylindrical body. It is often overlooked as it resembles a black earthworm, but it moves a lot faster. The snout and the tip of the tail (which ends in a spine) are usually of a paler colour. It burrows, and can be found under rocks and logs in the forest or even in gardens. It feeds on small soil-dwelling invertebrates. It is believed to be an all-female species that lay eggs.

Family Pythonidae

The pythons are usually large, muscular and non-venomous with heat-sensory pits along their upper lips to help them to detect warm-blooded prey. They kill their prey by wrapping their body around them and gradually constricting them until they suffocate. Some pythons have a pair of spurs on their pelvic region which are remnants of degenerate limbs.

The Reticulated Python (Broghammerus reticulatus) can grow to almost 10m, though those seen in Singapore are seldom more than 5m. It is one of the biggest snakes in the world. The body is greyish brown with networks of irregular black and yellow patterns. It is mostly nocturnal, and feed on small mammals and birds. It can be found on the ground or on trees in the forest, and is also a good swimmer. It can sometimes be found in urban areas too, such as in monsoon drains. It is oviparous.

Family Acrochordidae

The acrohordid snakes are mostly aquatic. They have rough, baggy skin, small eyes on smallish heads. They give birth to live young.

The Banded File Snake (Acrochordus granulatus) is usually black or dark grey with light grey, white or cream-coloured bands. It has very rough scales, and the skin appears to be hanging loose. It usually does not exceed 1m in length. This non-venomous snake can be found in coastal areas and river mouths, feeding on small fish and other marine animals.

Family Colubridae

Colubrid snakes have large forehead scales and lateral nostrils. They are generally rather diverse, and more studies need to be done on the group. They can be non-venomous or venomous.

The Oriental Whip Snake (Ahaetulla prasina) has a very slender body and a distinct head with a pointed snout (in side profile). The pupils of the eyes are horizontally elongated, compared to the the similar-looking Big-eye Whip Snake. Adult Oriental Whip Snakes are fluorescent green above, with a pair of yellow stripes, one on each side of the belly. Juvenile snakes may have paler colours or darker patches on the body. They are mostly found on trees and bushes in secondary forests or forest edges. Being mildly venomous, they hunt for small vertebrates such as lizards and frogs, usually in the day. They give birth to live young, and can grow to about 1.9m long.

The Big-eye Whip Snake (Ahaetulla mycterizans) appears very similar to the previous species, but has a pair of white (instead of yellow) stripes on its belly (one on each side). The pupils of the eyes often appear bigger than those of the previous species as well. Like the previous species, it is mildly venomous. This species gets to a maximum length of about 1m.

The Paradise Tree Snake (Chrysopelea paradisi) is black above with yellowish spots, sometimes with red patterns. Growing to about 1.3m, this snake is commonly seen in a variety of habitats, including mangrove forests, secondary forests, and even gardens and parks. It is mildly venomous, and usually hunts for small animals among trees and bushes in the day. One amazing characteristic of this snake is its ability to glide from tree to tree by launching itself into the air and flattening its body (much like a long kite). It is oviparous.

The Twin-barred Tree Snake (Chrysopelea pelias) is mostly seen on trees and bushes in the day. It has broad red saddles on its back which are separated by narrow black-edged whitish bands. This small snake (usually not more than 74cm long) is mildly venomous. Like the previous related species, it is oviparous and can glide by launching itself into the air and flattening its body.

The Painted Bronzeback (Dendrelaphis pictus) is commonly seen in back mangroves, secondary forests and even gardens and parks. Growing to about 1m long, it is bronze brown above, with a black stripe on each side of its head starting from the snout, passing through the eye towards the tail. There is usually a yellowish stripe on each side of the body. Believed to be non-venomous, it hunts for small vertebrates both on the trees and on the ground in the day. It is oviparous.

The Haas's Bronzeback (Dendrelaphis haasi) is usually found in mature forest. It has a very slender body, growing to about 95cm. Compared to the previous species, it has broader scales on its back, and has a faint cream stripe along its sides. It also has a narrow black stripe behind the eye that breaks into blotches on the side of the neck. This species was only described in 2008, and confirmed to occur in Singapore in 2011.

The Elegant Bronzeback (Dendrelaphis formosus) is mostly found on trees in mature forests. They are more active in the day, feeding on small lizards on the trees. Growing to about 1.4m long, it is bronze brown above with a broad black stripe on each side of the head and neck. The belly is yellowish green. It is oviparous.

The Orange-bellied Ringneck (Gongylosoma baliodeirum) is a small snake that can only grow to about 35cm long. It is usually found in mature forest, and can be recognised by the yellowish spots on the dark brown body. The underside is orange. It appears to be non-venomous.

The House Wolf Snake (Lycodon capucinus) is commonly seen in forested areas, gardens and even among human habitation. This small snake (up to about 75cm long) is usually chocolaty brown above with numerous cream-coloured bands, spots and patches. It feeds on small vertebrates such as geckos, and can be found on the ground as well as on trees at night. It is oviparous, and not known to be venomous.

The Gold-ringed Cat Snake (Boiga dendrophila) is very distinctive with its shiny black body marked with narrow, bright yellow bands. It can grow to 2.5m long, and is nocturnal. Usually found on trees and low bushes, it can sometimes be seen slithering on the ground or swimming in water at night as well, hunting for small vertebrates. This oviparous snake is mildly venomous

The Dog-toothed Cat Snake (Boiga cynodon) is mostly seen on trees and bushes, and occasionally on the ground. It can grow to about 2.7m, with a laterally compressed body and distinctive head. The body is yellowish or brown with irregular dark brown to black (mostly) cross bars. This oviparous snake is nocturnal and mildly venomous, usually feeding on birds and eggs.

The Pink-headed Reed Snake (Calamaria schlegeli) resembles the very venomous Blue Malayan Coral Snake, but lacks the bright blue stripes on the sides of the belly found on the latter. It is non-venomous, with a pinkish red head. It can grow to about 1.2m long. Like other reed snake, it is a burrower and feeds on small invertebrates. It is sometimes seen among the leaf litter, or on the forest floor at night.

The Malayan Racer (Coelognathus flavolineatus) is mostly terrestrial, and is sometimes encountered crossing the road in rural areas in the day. It can grow to about 1.8m long, with a dark brown body marked with black blotches and broken stripes. Sometimes, a pale stripe is present, running down the back of the animal. This oviparous snake appears to be non-venomous, and kill its prey (smaller vertebrates) by constriction.

The Red-tailed Racer (Gonyosoma oxycephalum) is largely arboreal, being usually found on trees. It can reach a length of 2.4m, with thick-set, laterally compressed body that is bright green above and pale green below. The tail is rusty brown or reddish. This oviparous snake is non-venomous, and hunts for birds and small mammals, killing them by constriction.

Family Homalopsidae

Homalopsid snakes generally live partly or entirely in water. They usually have reduced eyes, probably an adaptation to having to live in murky waters, and nostrils which can be closed by valve-like structures to prevent water from getting in. They are mildly venomous, and are ovoviviparous (as explained earlier, bear live young from eggs brood within the body).

The Dog-faced Water Snake (Cerberus schneiderii), or Schneider's Bockadam, has an olive to brown body with irregular narrow blackish bars. The eyes are small, situated near the top of its head, which will be useful for peeping above the water. This ovoviviparous snake can grow to about one metre long. It is mostly nocturnal, though sometimes it can be seen in the day when it cloudy. It can be seen in the water in mangroves or adjacent shores, or on land exposed during low tide. Being mildly venomous, it feeds on fish. The common name is derived from the side profile of its head, which resembles a dog's head. In fact, the genus, Cerberus, is a multi-headed hound in Greek mythology (and is also featured in Harry Potter as a three-headed dog).

Family Elapidae

Elapid snakes are reputed and much-feared for their lethal venom. The venom glands are connected to a pair of short, rigid fangs in the front of their upper jaws. They are usually more aggressive when they perceive threat, and hence it is important not to provoke them by keeping a good distance. In fact, most of the time, they will stay away from human, and will quickly slither away when they sense someone getting near.

The Blue Malayan Coral Snake (Calliophis bivirgata) is highly venomous (possessing neurotoxins), and advertises this with its striking colours. The head and tail are bright red, while the back is navy blue. A powder blue stripe runs along each side of the body. This snake can grow to about 1.8m long, and is usually found in mature forest, usually on the forest floor. While it is mostly nocturnal, it is also occasionally seen in the morning. This oviparous snake feeds on other snake. A bite from this snake can result in death. Its venom glands occupy almost a third of its body length.

The Equatorial Spitting Cobra (Naja sumatrana), also called the Black Spitting Cobra locally, can spit venom over a distance of more than a metre away. The venom can cause temporary blindness if it gets into the eye, and hence it is important to keep a good distance from any black snake that you cannot immediately identify. This cobra can get to about 1.5m long, and has a hood (stretchable fold of skin on both sides of the neck) which can be spread out. It will usually do this, and also raise the front part of body when provoked. This oviparous snake feeds on small vertebrates, and can be found in a variety of habitats, ranging from mangrove forest to wooded areas and scrubland, even those near human habitation. The above photo features an Equatorial Spitting Cobra feeding on an Asian Toad (Duttaphrynus melanostictus).

The Banded Krait (Bungarus fasciatus) is found in coastal and mangrove forests, inland forests and sometimes agricultural land, often close to water bodies. The body, which is triangular in cross-section, is marked with alternating black and yellow bands. It feeds on other snakes and lizards. While it is believed to be mostly nocturnal, it is sometimes seen slithering on the forest floor in the day. This oviparous snake is highly venomous, whose bite can be lethal.

Family Hydrophiidae

Hydrophiid snakes have short and flattened paddle-like tails, adapted for swimming in the sea. They are extremely venomous, possessing myotoxins that destroy muscle tissues, but are generally not aggressive.

The Amphibious Sea Snake (Laticauda colubrina), also called the Yellow-lipped Sea Krait, is the only hydrophiid sea snake that comes ashore occasionally to rest and lay eggs. The other sea snakes give birth to live young. The body of the Amphibious Sea Snake is bluish grey with black bands, and the immediate area around the mouth is yellow in colour. Like other sea snakes, its tail is flattened and paddle-like. It feeds on fish, and can grow to about 1.4m long. While sea snakes usually appear rather docile, they should never be handled due to the extremely toxic venom.

The Marbled Sea Snake (Aipysurus eydouxii) is usually seen in shallow waters and coral reefs, though sometimes it can be found stranded on the beach by the receding tides. This is a true sea snake that gives birth to live young out in the sea. This species is believed to feeds mostly on fish eggs. Like other sea snakes, its tail is flattened and paddle-like. It grows to about 1m long and can be recognised by the broad dark brown and thinner pale bands on the body. The toxicity of its venom has apparently been greatly reduced, suspected to be a result of its unusual diet.

Family Viperidae

Vipers can be recognised by their triangular heads and short, thick bodies. In Singapore, this family is represented by the pit-vipers, which have a heat-sensitive pit between the eyes and the nostrils for detecting warm-blooded prey. They are usually arboreal and have prehensile tails. They are mostly active at night, and rest on branches of trees in the day. They have a pair of long fangs on the upper jaw, which can deliver a haemotoxin that destroys red blood cells.

The Shore Pit Viper (Cryptelytrops purpureomaculatus) is usually found on trees coastal and mangrove forests, or sometimes among the rocks on rocky shores and sea walls. They have keeled scales, and the body is purplish black, grey or dark brown, often with irregular darker bands or patches. This venomous snake is nocturnal and live bearing. It is aggressive when provoked, and feed on small vertebrates. Adult snakes can be about 1m long.

The Wagler's Pit Viper (Tropidolaemus wagleri) is usually found in mature forests. The head is broadly triangular from top view, and like the previous species, it is covered with keeled scales. The females are black with greenish and yellow bands on its back, and yellow below.

The juvenile and male Wagler's Pit Vipers are green with pairs of green and red short bars sparsely spaced, running along the sides of their bodies. The bars tend to be longer on the adult males. Like other vipers, they are very venomous and hunt for small vertebrates at night. Like the previous species, they are live-bearing.